It is known that focusing means, such as refractive lenses and lens systems, cause both diffraction and aberration to occur in a beam of electromagnetic radiation with which is interacts.
It is also known that when the effective diameter of a beam of electromagnetic radiation which impinges on a focusing means is adjusted, the effects of diffraction and of aberration are affected oppositely. That is, as the beam cross-sectional area is increased, the effects of diffraction decrease, but the effects of aberration increase. This leads to a realization that, for each wavelength in the beam, there should be a beam cross-sectional area such that the focusing lens performs “optimally”. That is, there exists a cross-section area such that increase or decrease in cross-sectional area will cause combined diffraction or aberration to become worse, (ie. cause lens performance to be worse).
It is also well known that attenuation of the intensity of a beam of electomagnetic radiation which is caused to pass through a material is related to the extinction coefficient and thickness of the material via Beer's Law:Io=Ii(e−∝T).Therefore, either an increase in the value of extinction coefficient ∝, or a greater thickness (T) of a material, or a combination of both, can cause a greater attenuation of input intensity (Ii) of components of a beam of electromagnetic radiation which passes through a lens. This is to be contrasted with the situation where input Intensity (Ii) is attenuated by reflection or scattering from a surface of an aperture forming material. Further, it is noted that “reflection” implies a specular condition wherein an angle of incidence of an input beam of electromagnetic radiation component is equal to an angle of reflection; whereas “scattering”, while still indicating a deflection of a component of an electromagnetic beam away from transmission through a lens, does not have such a limitation on the angle at which a beam component is deflected.
With the present invention in mind a computer search for Patents and Published Applications was conducted. A few references were identified which are interesting as they relate to aberration corrections. For instance, a patent to Lee et al., U.S. Pat. No. 6,994,808 describes a planar lens which is designed to compensate chromatic aberration. Another patent to Kimura, U.S. Pat. No. 6,865,025 provides another optical element for application in compensating aberration. And, a Published Patent Application by Miller et al., No. 2004/0032664 describes a color corrected lens. Other Patents and Published Applications identified are: